After four years of erratic and increasingly tyrannical rule, Caligula was ambushed by Praetorian Guard officers, led by Cassius Chaerea, a tribune he had repeatedly mocked. The assassination plunged the palace into chaos, and his uncle Claudius, discovered hiding behind a curtain by a soldier, was declared the next emperor almost by accident.

After a brief and extraordinary trial in which Charles I refused to recognize the court's authority to try an anointed monarch, the tribunal established by Parliament pronounced him guilty of tyranny and treason. The verdict, reached in the days around January 24, set the stage for his beheading on January 30 — the first execution of a reigning English monarch.

Weeks after former President John Quincy Adams argued their case before the Supreme Court, the Africans who had mutinied aboard the slave ship Amistad were declared free men, having been illegally kidnapped rather than lawfully enslaved. The ruling, delivered in the weeks around January 1841, became a rallying point for the American abolitionist movement.

While inspecting a sawmill he was building for John Sutter, carpenter James Marshall noticed glinting metal in the millrace and realized it was gold. News spread slowly at first, but within a year tens of thousands of prospectors from across the world had poured into California, permanently transforming its economy, population, and place in the American imagination.